Congenital malformations of the lungs
The concept of congenital malformations of the lungs is inextricably linked with the understanding of the basic patterns of the formation of the bronchopulmonary system. The lung of a person is formed continuously, starting from the earliest stages of intrauterine development, and continues throughout the entire period of childhood.
Three periods, or stages, of embryonic development of the lung are distinguished: glandular, when airway pathways develop;canalicular, corresponding to the formation of respiratory( respiratory) bronchioles, and alveolar, when alveolar courses and alveoli are formed.
Primary lung rudiment is detected in a 3-week embryo having a length of only 3 mm. In the embryo 4 mm in length( the gestation period is 1 week), rudiments are formed, which subsequently lead to the formation of the main bronchi. At the 5th week these rudiments continue to grow, giving rise to shared bronchial tubes. At the 6-7th week of intrauterine development, there are the main bronchi and the rudiments of segmental bronchi, and by 8 weeks - the branching of subsegmental bronchi.
Parallel with the formation of the first bronchi for each lung, pulmonary arteries differentiate. At the 6-7th week arterial system of a small circle of blood circulation arises. Pulmonary veins appear in the tissue of the lung rudiment and grow towards the heart. By the end of the third month of intrauterine development, the large bronchi have structural elements of all three membranes that form them. At the same time, the formation of bronchial glands begins. At the 5th-6th month of embryonic development, small bronchi appear, as well as respiratory bronchioles. The lungs at this time are a well-supplied blood organ, since in no other gland embryonic period there is such a developed network of blood vessels. By 7 months of embryonic development, the structure of the respiratory tract is already capable of providing gas exchange processes. The formation of the alveoli begins at the beginning of the 8th month of the intrauterine period. From this time, the fetal lung acquires such a structure, which is present at the birth of the child.
A stop or violation of embryonic development of the respiratory system is possible at various stages of its formation. This determines the diversity and nature of the vices. Thus, the arrest of development at the level of the primary rudiment determines the bilateral absence( bilateral agenesis) of the lungs. The developmental disorder at the 4th week of the embryonic period determines the unilateral absence or underdevelopment of the lung. Such defects as polycystosis, branching anomalies, arise in later periods of embryonic life.
The formation of the lung continues after the birth of the child. In the first 10 years of life the lung intensively grows, the number of alveoli progressively increases, new bronchial branches appear. Defects in the development of the bronchopulmonary system in a large number of cases are the basis for the formation of recurrent( ongoing with periodic exacerbations) and chronic lung diseases in the child. According to the information available in the literature, developmental defects are diagnosed in 10-15% of people suffering from chronic lung diseases. In the development of these defects the leading role is assigned to hereditary factors. It is believed that the contribution of these factors to the origin of vices is greater than 75-80%.Defects can be the result of gene mutations, chromosomal abnormalities, and also have a multifactorial origin, i.e., develop as a result of the influence of a large number of factors.
Malformations of the lung clinically usually do not occur before any infection is layered. Attachment of infection turns the carrier of a defect into a patient with chronic pneumonia.